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Register a new userPhonon confinement and plasmon-phonon interaction in nanowire based quantum wells
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Resonant Raman spectroscopy is realized on closely spaced nanowire based quantum wells. Phonon quantization consistent with 2.4 nm thick quantum wells is observed, in agreement with cross-section transmission electron microscopy measurements and photoluminescence experiments. The creation of a high density plasma within the quantized structures is demonstrated by the observation of coupled plasmon-phonon modes. The density of the plasma and thereby the plasmon-phonon interaction is controlled with the excitation power. This work represents a base for further studies on confined high density charge systems in nanowires.
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The extraordinary properties of two dimensional (2D) materials, such as the extremely high carrier mobility in graphene and the large direct band gaps in transition metal dichalcogenides MX2 (M = Mo or W, X = S, Se) monolayers, highlight the crucial role quantum confinement can have in producing a wide spectrum of technologically important electronic properties. Currently one of the highest priorities in the field is to search for new 2D crystalline systems with structural and electronic properties that can be exploited for device development. In this letter, we report on the unusual quantum transport properties of the 2D ternary transition metal chalcogenide - Nb3SiTe6. We show that the micaceous nature of Nb3SiTe6 allows it to be thinned down to one-unit-cell thick 2D crystals using microexfoliation technique. When the thickness of Nb3SiTe6 crystal is reduced below a few unit-cells thickness, we observed an unexpected, enhanced weak-antilocalization signature in magnetotransport. This finding provides solid evidence for the long-predicted suppression of electron-phonon interaction caused by the crossover of phonon spectrum from 3D to 2D.
Recent progress in the fabrication of materials has made it possible to create arbitrary non-periodic two-dimensional structures in the quantum plasmon regime. This paves the way for exploring the plasmonic properties of electron gases in complex geometries such as fractals. In this work, we study the plasmonic properties of Sierpinski carpets and gaskets, two prototypical fractals with different ramification, by fully calculating their dielectric functions. We show that the Sierpinski carpet has a dispersion comparable to a square lattice, but the Sierpinski gasket features highly localized plasmon modes with a flat dispersion. This strong plasmon confinement in finitely ramified fractals can provide a novel setting for manipulating light at the quantum scale.
Plasmon and coupled plasmon-phonon modes in graphene are investigated the-oretically within the diagrammatic self-consistent field theory. It shows that two plasmon modes and four coupled plasmon-phonon modes can be excited via intra-and inter-band transition channels. It is found that with increasing q and carrier density, the plasmon modes couple strongly with the optic-phonon modes in graphene. The coupled plasmon-phonon modes exhibit some interesting features which can be utilized to realize the plasmonic devices. Our results suggest that the carrier-phonon interaction should be considered to understand and explain the properties of elementary electronic excitations in graphene.
Suppressing phonon propagation in nanowires is an essential goal towards achieving efficient thermoelectric devices. Recent experiments have shown unambiguously that surface roughness is a key factor that can reduce the thermal conductivity well below the Casimir limit in thin crystalline silicon nanowires. We use insights gained from the experimental studies to construct a simple analytically tractable model of the phonon-surface roughness interaction that provides a better theoretical understanding of the effects of surface roughness on the thermal conductivity, which could potentially help in designing better thermoelectric devices.
Spin-phonon interaction is an important channel for spin and energy relaxation in magnetic insulators. Understanding this interaction is critical for developing magnetic insulator-based spintronic devices. Quantifying this interaction in yttrium iron garnet (YIG), one of the most extensively investigated magnetic insulators, remains challenging because of the large number of atoms in a unit cell. Here, we report temperature-dependent and polarization-resolved Raman measurements in a YIG bulk crystal. We first classify the phonon modes based on their symmetry. We then develop a modified mean-field theory and define a symmetry-adapted parameter to quantify spin-phonon interaction in a phonon-mode specific way for the first time in YIG. Based on this improved mean-field theory, we discover a positive correlation between the spin-phonon interaction strength and the phonon frequency.
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